Systems and Methods for Mobile Stations to Identify Radio Access Technologies

ABSTRACT

A mobile station capable of being served via a first radio access technology (RAT) and a second RAT. The mobile station includes a component configured to receive a permission to identify a cell of the first RAT in absence of a first radio access type neighbour cell list for a serving cell of the second RAT. The mobile station also includes a component configured to identify a cell of the first RAT after receiving the permission.

PRIORITY CLAIM

This application is a divisional of application Ser. No. 12/435,357,filed May 4, 2009, which is incorporated herein by reference in itsentirety.

BACKGROUND

As used herein, the terms “mobile station” (“MS”) and “user equipment”(“UE”) might in some cases refer to mobile devices such as mobiletelephones, personal digital assistants, handheld or laptop computers,and similar devices that have telecommunications capabilities. Such a MSmight consist of a MS and its associated removable memory module, suchas but not limited to a Universal Integrated Circuit Card (UICC) thatincludes a Subscriber Identity Module (SIM) application, a UniversalSubscriber Identity Module (USIM) application, or a Removable UserIdentity Module (R-UIM) application. As used herein, the term “SIM” mayalso refer to “USIM” and the term “USIM” may also refer to “SIM.”Alternatively, such a MS might consist of the device itself without sucha module. In other cases, the term “MS” might refer to devices that havesimilar capabilities but that are not transportable, such as desktopcomputers, set-top boxes, or network appliances. The term “MS” can alsorefer to any hardware or software component that can terminate acommunication session for a user. Also, the terms “MS,” “UE,” “useragent” (“UA”), “user device” and “user node” might be used synonymouslyherein.

As telecommunications technology has evolved, more advanced networkaccess equipment has been introduced that can provide services that werenot possible previously. This network access equipment might includesystems and devices that are improvements of the equivalent equipment ina traditional wireless telecommunications system. Such advanced or nextgeneration equipment may be included in evolving wireless communicationsstandards, such as long-term evolution (LTE). For example, an LTE systemmight include an enhanced node B (eNB), a wireless access point, or asimilar component rather than a traditional base station.

As used herein, the term “access node” will refer to any component ofthe wireless network, such as a traditional base station, a wirelessaccess point, or an LTE eNB, that creates a geographical area ofreception and transmission coverage allowing a MS or a relay node toaccess other components in a telecommunications system. In thisdocument, the term “access node” may comprise a plurality of hardwareand software. An access node, core network component, or other device,may provide wireless communications resources in an area known as acell.

An LTE system can include protocols such as a Radio Resource Control(RRC) protocol, which is responsible for the assignment, configuration,and release of radio resources between a MS and an access node or relaynode or other LTE equipment. The RRC protocol is described in detail inthe Third Generation Partnership Project (3GPP) Technical Specification(TS) 36.331.

The signals that carry data between MSs, relay nodes, and access nodescan have frequency, time, and coding parameters and othercharacteristics that might be specified by a network node. A connectionbetween any of these elements that has a specific set of suchcharacteristics can be referred to as a resource. The terms “resource,”“communications connection,” “channel,” and “communications link” mightbe used synonymously herein. A network node typically establishes adifferent resource for each MS or other network node with which it iscommunicating at any particular time.

Different types of radio access technologies (RATs) have been developedand used. An example of a RAT is a “GERAN,” which is “GSM/EDGE” radioaccess network. “GSM” is “global system for mobile communications.”“EDGE” is “Enhanced Data Rates for GSM Evolution,” which is a type ofwireless communication network. As used herein, the term “GERAN” may beread to include UTRAN. “UTRAN” is “universal terrestrial radio accessnetwork.”

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is nowmade to the following brief description, taken in connection with theaccompanying drawings and detailed description, wherein like referencenumerals represent like parts.

FIG. 1 is a diagram illustrating a wireless communication system,according to an embodiment of the disclosure.

FIG. 2 is a diagram illustrating a wireless communication system,according to an embodiment of the disclosure.

FIG. 3 is a flowchart illustrating a process of a MS performingundirected searching and subsequent reselection, according to anembodiment of the disclosure.

FIG. 4 is a flowchart illustrating a method for granting a MS permissionto search one or more E-UTRAN frequencies while in a GERAN cell,according to an embodiment of the disclosure.

FIG. 5 is a flowchart illustrating a method for granting an MSpermission to search one or more E-UTRAN frequencies while in a GERANcell, according to an embodiment of the disclosure.

FIG. 6 is a block diagram illustrating a MS communicating with a corenetwork via a radio access network, according to an embodiment of thedisclosure.

FIG. 7 illustrates a processor and related components suitable forimplementing the several embodiments of the present disclosure.

DETAILED DESCRIPTION

It should be understood at the outset that although illustrativeimplementations of one or more embodiments of the present disclosure areprovided below, the disclosed systems and/or methods may be implementedusing any number of techniques, whether currently known or in existence.The disclosure should in no way be limited to the illustrativeimplementations, drawings, and techniques illustrated below, includingthe exemplary designs and implementations illustrated and describedherein, but may be modified within the scope of the appended claimsalong with their full scope of equivalents.

As used herein, the following acronyms have the following definitions.

“AS” is defined as “access stratum,” which comprises one or more radioaccess and/or radio management layers in a protocol stack in a MS orradio access network (RAN).

“ARFCN” is defined as “absolute radio frequency channel number,” whichis a number that identifies a mobile communications frequency, and maybe used to identify a mobile communications cell when referring to theARFCN of the BCCH carrier of a cell.

“BCCH” is “broadcast control channel,” which is a mobile communicationsresource.

“BSC” is “base station controller.”

“BSS” is “base station subsystem.”

“BTS” is “base transceiver station.”

“CCO” is “cell change order.”

“CN” is defined as “core network,” which refers to devices and softwarefor processing messages and data from MSs (mobile stations), sentthrough radio access networks (RANs).

“CS” is defined as “circuit switched,” which refers to a conventionalprocedure for communicating a phone call or for connecting devices fordata transfer over a permanent or semi-permanent radio connection, suchas, for example, a telephony line.

“CSFB” is defined as “CS fallback,” which refers to a procedure inwhich, when implementing a communication, an evolved packet system (EPS)enabled device “falls back” to a circuit switched (CS) communicationprocedure.

“DL” is “downlink”

“DLDC” is “downlink dual carrier.”

“DTM” is “dual transfer mode.”

“EARFCN” is defined as the E-UTRAN absolute radio frequency channelnumber, which refers to a number that identifies a frequency in anE-UTRAN wireless communication network.

“eNB,” as defined above, is an “enhanced node B,” which is an example ofone type of device used in a radio access network (RAN) to aid inestablishing communication between a MS and a CN.

“EPC” is defined as “evolved packet core,” which refers to the corenetwork (CN) to which a long term evolution (LTE) radio networkcommunicates.

“EPS” is defined as “evolved packet system,” which refers to the EPC anda set of access systems—EPS represents the system that may have theE-UTRAN as a radio network, and the EPC as its core network.

“E-UTRAN,” is defined as “evolved UTRAN,” which refers to “evolved UMTSterrestrial RAN,” which in turn refers to, “evolved universal mobiletelecommunications system terrestrial radio access network;” E-UTRANrefers to the network of “e-NBs” (“enhanced node-Bs”) in a long termevolution (LTE) communications system. As used herein, the terms“E-UTRAN” and “LTE” may be used interchangeably.

“GPRS” is “general packet radio service,” which is a system used by GSMMSs.

“IMS” is “IP (Internet protocol) multimedia subsystem.”

“LAU” is “location area update.”

“LTE” is defined as “long term evolution,” which refers to a newersystem of high speed mobile communications and infrastructure.

“NAS” is defined as “non-access stratum,” which is a layer in a protocolstack in both a MS and a core network (CN), but may not be in a protocolstack of a radio access network (RAN).

“MAC” is defined as “medium access control,” which is a protocol layerin a MS, and RAN.

“MME” is “mobility management entity.”

“MO data” is defined as “mobile originating data,” which is a type ofestablishment cause used in EPS-enabled systems.

“MO signaling” is defined as “mobile originating signaling.”

“MS” is “mobile station.”

“MSC” is “mobile switching center.”

“MT access” is defined as “mobile terminating access.”

“NACC” is “network assisted cell change.”, which is a method ofproviding system information corresponding to a second cell to a MS in afirst cell

“NCL” is “neighbour cell list.”

“NMO” is “network mode of operation.”

“NPM” is “non-persistent mode.”

“PCI” is “physical cell identity.”

“PLMN” is “public land mobile network.”

“PS” is “packet switched.”

“RA” is “routing area.”

“RAN” is defined as “radio access network.”

“RAT” is “radio access technology,” examples of which include GSM, EDGE,E-UTRAN, UMTS, and LTE.

“RAU” is “routing area update.”

“RLC” is “radio link control.”

“RR” is “radio resource.”

“RRC” is “radio resource control.”

“RTTI” is “reduced transmission time interval,” which is part of a GERANlatency reduction feature.

“S-GW” is “signaling gateway”.

“TAU” is “tracking area update.”

“TBF” is “temporary block flow.”

“TCP” is “transmission control protocol.”

“TS” is defined as “technical specifications,” which are mobilecommunications specifications called-for by the 3GPP (3^(rd) generationpartnership project).

“UL” is “uplink”.

“USF” is “uplink state flag.”

“TDMA” is “time division multiple access.”

Other acronyms that may appear herein are used and defined according tothe technical specifications of the 3GPP standards.

The embodiments described herein provide for devices and methods forallowing a MS to overcome being constrained. “Constrained” is defined asa situation in which a MS, either in idle mode or active mode, that isenabled to communicate in both a first radio access technology systemand a second radio access technology system, and that is being served bya mobile communication cell of the second RAT, but the MS is unable, forwhatever reason, to connect to a mobile communication cell of the firstRAT that is otherwise available to the MS. An example of a MS beingconstrained includes a MS being unaware of the presence of a cell, evenif potential reception of the cell is good. In an embodiment, anE_UTRAN-capable MS can become constrained on a GERAN cell, even thoughthe MS preferably should be connected to an E-UTRAN cell, and thecoverage of the E-UTRAN cell overlaps that of the GERAN cell.

As a non-limiting summary of the above definition, an E-UTRAN-capable MSis “constrained” if the MS is connected to a GERAN network, but isunable to connect to an otherwise available E-UTRA network. A MS is saidto be “unconstrained” for those situations in which a MS overcomes beingconstrained, and is thus able to reselect to the E-UTRA network.

Specifically, the embodiments provide for the MS performing anundirected attempt to identify one or more E-UTRAN cells. In someembodiments, the undirected search might be performed according to theprocedures and/or rules described herein. The term “undirectedsearching” refers to a MS wirelessly searching for a resource of anetwork, or for a particular access node or base station, without havingreceived any prior identification or knowledge of the existence of sucha network, access node, or base station by means of a neighbour celllist specified primarily for the indicating the presence of suchnetwork, access node, or base station. The purpose of the process ofsearching is to identify a cell. The identification of a cell may bedone by recognition of a specific physical layer aspect of the networktransmission, by the recognition of specific control channels or beaconsdesign for this purpose, or by explicitly reading a field whichidentifies the cell as belonging to a specific network. For example inE-UTRAN if the MS knows the center frequency it attempts to detect theprimary and secondary synchronization signals. The combination ofprimary and secondary synchronization signals gives the MS the physicalcell ID (PCI) which is locally unique. The MS can then read the systeminformation to obtain a CGI (cell global identity). Only detection ofthe locally unique PCI is required for cell reselection and measurementpurposes. If the MS does not know the centre frequency it must attemptto perform the above synchronization process on every potential centerfrequency on a 100 kHz raster within the frequency bands supported bythe UE. The UE might do some wideband RSSI measurement to judge if thereis any RF energy before attempting the synchronization process on agiven center frequency to minimize the searching time but this isimplementation specific.

The MS might be required to perform an undirected search only if the MSreceives permission to attempt to identify an E-UTRAN cell.Additionally, the MS might be required to perform a subsequent cellreselection upon receiving permission. Permission for conducting anundirected search and permission for cell reselection may be providedaccording to a number of different techniques, as described furtherbelow.

The embodiments allow a MS to reselect a cell, even though suchreselection might not be possible according to existing reselectionrules. MS reselection might not be possible because, under existingreselection rules, the neighbour cell list of a serving cell might notlist an E-UTRAN cell, or its center frequency. Having the MS conduct thesearch and subsequently reselect to the E-UTRAN cell reduces the needfor operators to ensure that all network equipment is upgraded or fullyupdated when adding E-UTRAN coverage to a geographical area, while stillproviding a good user experience by allowing the user to more easilytake advantage of high-bandwidth E-UTRAN networks.

In the embodiments described above and below, the permissions and/or MSbehavior to be specified might be directly in response to explicitsignaling. These permissions need not necessarily be transmitted and/orreceived, but may be based on rules stored in the MS, as is the casecurrently for reselection rules. In other words, there may be rulesdetailed in the 3GPP standards which trigger the MS to conduct anundirected search and/or to reselect an E-UTRAN cell.

While the embodiments are described with respect to particular types ofradio access technologies (RATs), such as GERAN, UTRAN, and E-UTRAN, theembodiments may also apply to other kinds of wireless communicationnetworks. Therefore, the embodiments apply to MSs that might becomeconstrained on a first network when the MSs should or could connect toan otherwise available second network.

FIG. 1 is a diagram illustrating a wireless communication system,according to an embodiment of the disclosure. FIG. 1 shows a MS 100,which could be system 715 of FIG. 7. The MSs described herein areoperable for implementing aspects of the disclosure, but the disclosureshould not be limited to these implementations. Though illustrated as amobile phone, the MSs may take various forms including wirelesshandsets, a pager, personal digital assistants (PDAs), portablecomputers, tablet computers, or laptop computers. Many suitable devicescombine some or all of these functions. In some embodiments of thedisclosure, the MSs are not general purpose computing devices likeportables, laptops or tablet computers, but rather are special-purposecommunications devices, such as mobile phones, wireless handsets,pagers, or PDAs. In other embodiments, MSs may be portable, laptops, orother computing devices.

Among the various applications executable by the MSs are web browsers,which enable displays to show web pages. Web pages may be obtained viawireless communications with wireless network access nodes, cell towers,peer MSs, or any other wireless communication network or systems.Networks may be coupled to wired networks, such as the Internet. Via awireless link and a wired network, MSs may have access to information onvarious servers. Servers may provide content that may be shown on thedisplays. Alternately, MSs may access networks through peer MSs actingas intermediaries, in relay type or hop type connections.

MS 100 is capable of communicating with both an E-UTRAN access node 102(as shown by arrows 102A), and with a GERAN/UTRAN access node 106, asshown by arrows 106A. E-UTRAN access node 102 provides wirelesscommunication resources in E-UTRAN cell 104, and the GERAN/UTRAN accessnode 106 provides wireless communication resources in a GERAN or UTRANcell 108. Although in the embodiments E-UTRAN access node 102establishes an E-UTRAN network, E-UTRAN access node 102 may representany LTE access node and corresponding LTE cell. Likewise, although inthe embodiments GERAN/UTRAN access node 106 establishes a GERAN or UTRANnetwork, GERAN/UTRAN access node 106 may represent any non-LTE accessnode and corresponding non-LTE cell.

In an embodiment, MS 100 may find itself being served by GERAN cell 108,but that cell does not indicate the presence of E-UTRAN cell 104 orother E-UTRAN cells in the neighbourhood of GERAN cell 108. MS 100should be able to connect to E-UTRAN access node 102 because MS 100 isin both E-UTRAN cell 104 and GERAN cell 108, and further because MS 100is an E-UTRAN-capable device.

However, the MS may be unable to select the E-UTRAN cell because thereselection and measurement procedures may only allow for the MS toreselect cells which are indicated by a neighbour cell list of thecurrent (serving) cell. Presently, the MS may not be permitted toreselect an E-UTRAN cell if the serving cell, such as a legacy accessnode, has not been upgraded or updated to indicate the presence ofE-UTRAN neighbour cells. In other words, an LTE-capable MS can becomeconstrained on a GERAN cell, even though the MS preferably should beconnected to an E-UTRAN cell that overlaps the GERAN cell. Thissituation is undesirable because E-UTRAN access node 102 may be able toprovide higher peak data rates or significantly lower latency relativeto that which can be provided by GERAN/UTRAN access node 106.

An example of a situation in which MS 100 may become constrained isafter the MS 100 is involved in a CS fallback communication. A CSfallback communication can occur in situations in which E-UTRAN accessnode 102 is incapable of handling a certain kind of communication, suchas a voice communication, or generally in situations in which aGERAN/UTRAN access node 106 is better able to or otherwise should handlea particular communication. In this case, the MS 100 which waspreviously served by E-UTRAN cell 104 instead “falls back” to useGERAN/UTRAN access node 106 for that particular communication. The CSfallback communication procedure is described more fully with respect toFIG. 6 and is described in detail in 3GPP TS 23.272.

Another situation in which MS 100 may become constrained is when the MS100 moves from a physical location in which MS 100 is only within GERANcell 108 to a second physical location in which the MS 100 is withinboth E-UTRAN cell 104 and GERAN cell 108. This situation is shown by MS110A and MS 110B, the movement of which is shown by the arrow betweenthem. Once MS 110B is within both E-UTRAN cell 104 and GERAN cell 108,MS 110B should be able to connect to E-UTRAN access node 102, butinstead may be constrained because presently the MS is unaware of theE-UTRAN cell 104 based on information provided to it by its servingGERAN/UTRAN access node 106.

Yet another situation in which MS 100 may become constrained is where anetwork node, such as E-UTRAN access node 102 or E-UTRAN cell 104 orpossibly GERAN cell 108, transmits a neighbour cell list that isincomplete. For example, one or more cells which could provide a serviceto MS 100 are omitted from the neighbour cell list.

Still further, a MS which is being served by GERAN/UTRAN access node106, but which observes that there are no E-UTRAN frequencies listed inthe neighbour cell list sent by the GERAN/UTRAN access node 106, cannotdetermine whether the lack of such frequencies is due to the GERAN/UTRANaccess node 106 being a release-7 or earlier version (and therefore notsupporting E-UTRAN frequencies in the neighbour cell list), or becauseno such frequencies exist, or for some other reason, such as if theGERAN/UTRAN access node 106 is a release-8 or newer version but not yetconfigured to list E-UTRAN neighbour cells. A release-7 or earlier GERANaccess node currently does not list the frequencies of neighbour E-UTRANcells, whereas a release-8 or newer GERAN access node is so capable ifit has received the appropriate upgrade and configuration.

As indicated above, release-8 and newer GERAN/UTRAN base stations havethe capability to be aware of E-UTRAN by maintaining an E-UTRANneighbour cell list. These stations may send this information to the MS.However, older GERAN/UTRAN base stations may not be able to assist theMS with any information about E-UTRAN neighbour cells to measure forreselection. E-UTRAN cells may be identified by EARFCN and PCI. TheE-UTRAN neighbour cell information may include information such ascarrier frequencies identified by EARFCN, in which case the MS canconsider that any cell identified on that carrier frequency (and notexplicitly indicated as a not allowed cell) is a candidate forreselection.

Additional situations can arise in which MS 100 or MS 110B becomeconstrained. However the MS becomes constrained, the problem of beingconstrained has at least two aspects. In a first aspect, if the MS isbeing served by a GERAN/UTRAN cell and is not aware of the presence ofE-UTRAN neighbour cells, the MS should have some basis for determiningwhether to attempt to identify E-UTRAN cells. In a second aspect, oncethe MS has searched for E-UTRAN neighbour cells, the MS should have somebasis for determining whether to reselect to an E-UTRAN cell.Preferably, for both aspects, the network operator should have at leastsome control over the behavior of the MS.

While a constrained MS might be able to autonomously determine when toattempt to identify and reselect to an E-UTRAN cell, this solution maynot be preferred because the operator might desire to have some degreeof control over MSs switching from one cell to another. Additionally, aMS that autonomously searches for E-UTRAN cells may undesirably drain MSbattery power, particularly in those cases where an E-UTRAN cell may notbe available.

The present disclosure provides embodiments for allowing a MS toovercome being constrained. Specifically, the embodiments provide forthe MS performing an undirected or directed attempt to identify one ormore E-UTRAN cells according to various procedures described herein. Forexample, the MS may perform an undirected search if the MS receivespermission to attempt to identify any E-UTRAN frequency or cell.Alternatively, the MS may perform a directed search if the MS receivespermission to attempt to identify a specific E-UTRAN frequency or cell.Additionally, the MS may perform a subsequent cell reselection uponreceiving permission. Permission for conducting an undirected ordirected search and permission for cell reselection may be providedaccording to a number of different techniques, described below. Asdefined above, the term “undirected searching” refers to a MS wirelesslysearching for a resource of a network, or for a particular access nodeor base station, without having received any prior identification orknowledge of the existence of such a network, access node, or basestation by means of a neighbour cell list specified primarily for theindicating the presence of such network, access node, or base station.

The term “directed searching” refers to a MS wirelessly searching for aresource of a network, or for a particular access node or base station,having received some identification or knowledge of the existence ofsuch a network, access node, or base station by means of one or moreunused GERAN/UTRAN cell identities which the MS and the network haveassociated with one or more E-UTRAN frequencies or cell identities,however this knowledge of the existence of such a network, access node,or base station is not received via a neighbour cell list specifiedprimarily for the indicating the presence of such network, access node,or base station.

Permission To Perform Undirected or Directed Searching:

A variety of rules and/or indications may be used to determine when theMS is to perform an undirected or directed attempt to identify E-UTRANcells. The following rules may be combined into a variety ofcombinations of rules. Some of the following rules are intrinsic to theMS. Some of the following rules are transmitted at some point by theaccess node to the MS. Transmitted rules may be transmitted in broadcastsignaling, such as in system information messages or system informationblocks, or may be transmitted by means of point-to-point messages, suchas a packet measurement order. However, transmitted, received, orstored, the rules are not necessarily static, but could change.Furthermore different rules could be transmitted by the access node tothe MS in all of various types of signaling (broadcast, multicast,point-to-point, etc.), as well as via an OMA DM (open mobile alliancedevice management) object or via NAS signaling, etc. Thus, the operatormay have the ability to, at any time, change the rules for undirected ordirected searching and for reselection.

An example of a rule might be that permission to perform undirected ordirected searching may be signaled by a previous serving E-UTRAN cell.In this case, an E-UTRAN cell in which a MS has been previously campedmay explicitly signal that the MS is permitted to perform undirectedsearching when the MS is constrained. The E-UTRAN cell may also indicateone or more E-UTRAN frequencies to assist (i.e. direct) the MS inperforming the search.

Another example of a rule is that permission to perform undirected ordirected searching may be signaled by a GERAN cell. A release-8 or newerGERAN cell in which a MS has been previously camped, or in which the MSis currently camped, may explicitly signal that the MS is allowed toperform an undirected or directed search. This indication may include anindication which does not require release-8 or later functionalityassociated with the E-UTRAN interworking in the GERAN cell. For example,the GERAN BSS (such as GERAN/UTRAN access node 106) may provide a cellidentity that references a GERAN cell that does not actually exist. Thiscell identity is known to the MS to correspond to one or more E-UTRANfrequencies. Thus, the MS knows that the MS may be within coverage ofone or more E-UTRAN cells, and that the MS may perform undirected ordirected searching. When used by a release-8 or newer GERAN BSS, thisindication may allow the MS to distinguish between the case where theremay be E-UTRAN coverage in the neighbourhood, but the BSS has not beenconfigured to transmit the information, and the case where the BSS isconfigured to indicate explicitly that there is no E-UTRAN coverage inthe neighbourhood.

Yet another example of a rule is that permission to perform directedsearching may be indicated by the GERAN/UTRAN access node 106 sending aPACKET CELL CHANGE ORDER message to the MS. This message indicates acell identity that references a GERAN cell that does not actually exist(e.g. a “E-UTRAN-indicative” ARFCN), which the MS would identify as an“equivalent EARFCN” from mapping information obtained in a mannerdescribed below with respect to mapping of E-UTRAN-indicative ARFCN toE-UTRAN frequencies. In another embodiment of permission to perform anundirected search, permission in the form of one or more cell identitiesthat reference GERAN cells that do not actually exist (e.g.“E-UTRAN-indicative ARFCNs”) that might not be mapped to one or moreE-UTRAN frequencies, but may instead provide the permissions to conductan undirected attempt to identify an E-UTRAN cell, to reselect anE-UTRAN cell, or both.

In still another example of a rule, permission to perform undirectedsearching may be based on dedicated priorities previously received bythe MS. For example, the MS may have previously received dedicatedpriority information which includes a priority for one or more E-UTRANfrequencies. Examples of dedicated priority information may be found insub-clause 12.50 in 3GPP TS 44.060 version 8.4.0. Based on thisinformation, the MS may determine whether or not the MS is permitted toattempt to identify E-UTRAN cells.

Another example of a rule is that permission to perform undirectedsearching may be based on the use of a CS fallback procedure. In thisexample, the MS performs undirected searches for E-UTRAN cells in anycase where the MS has terminated a voice call or other CS domain servicewhich was initiated by means of a CS fallback procedure. Generally, thisrule may be used where the original change of radio access technology(RAT) was specifically for the purpose of using CS domain services.

Yet another example of a rule is that permission to perform undirectedsearching may be based on mobility and/or cell changes. In this case,the MS determines whether to perform undirected searching based on thenumber of cell changes since the MS was last served by an E-UTRAN cell.For example, the MS may perform undirected searching only if the MS iscurrently being served by the same cell that served the MS when the MSfirst left E-UTRAN service. Alternatively, the MS may perform undirectedsearching only if the MS remains within the same location area orrouting area as when the MS initially left E-UTRAN service.Alternatively, the MS may perform undirected searching only if the MSremains within the same PLMN as when the MS initially left E-UTRANservice. Alternatively, the MS may perform undirected searching only ifthe MS has moved a predetermined (or fewer) number of GERAN cells sinceleaving an E-UTRAN service.

In still another example of a rule is that permission to performundirected searching may be based on NAS signaling. The networkcommunicates whether the MS may perform undirected searching by means ofnon-access stratum (NAS) signaling. NAS signaling is described in moredetail with respect to FIG. 6. For example, during a routing area update(RAU) procedure, tracking area update (TAU) procedure, combined attachprocedure, or some other use of the NAS, the CN may provide additionaldata to the MS that permits the MS to perform undirected searching.

An additional example of a rule is that permission to perform undirectedsearching may be provided during provisioning or during over-the-airupdates. In this embodiment, permission to perform undirected searchingis stored in the MS, either in the USIM, SIM, or in some other memory ofthe MS. This permission may be set by the operator during provisioning,or may be communicated to the MS via over-the-air (OTA) updates. Oncethe permission is active, the MS subsequently has permission to performundirected searching.

In yet another embodiment, permission to perform undirected searchingmay be defined by user preference, or may be user-initiated. In thiscase, the MS determines whether to perform undirected searching based onone or more inputs by the user. The user-defined rule or rules toperform undirected searching can be further refined according to time,geographical location, operator input, application(s) in use, otherfactors, or combinations thereof.

In another embodiment, permission to perform undirected searching may bebased on voice service availability in E-UTRAN. In this case, the MS maytake into account the success or failure of previous attempts to performa combined attach procedure in an EPS. For example, the MS may notperform an undirected search in the case where the MS failed its mostrecent attempt to perform the combined attach procedure in EPS (which isa prerequisite for the CS fallback procedure). On the other hand, the MSmay perform undirected searching if the most recent combined attachprocedure was successful.

In still another embodiment, permission to perform undirected searchingmay be based on IMS/CSFB preference and/or the support of these featuresin the MS and/or the network. In this case, the MS takes account of itscapability and/or preference for initiating voice services while servedby an E-UTRAN network using IMS and/or by means of CSFB (CS fallback).For example, a MS which prefers, or is only capable of, initiating voicecommunication by means of CSFB may prefer to remain camped on a GERAN orother non-E-UTRAN cell. In this case, the MS may not perform undirectedsearching. Alternatively, a MS which is capable of IMS voicecommunication may perform undirected searching.

A number of considerations should be taken into account when performingundirected searches. In an embodiment, because the number of operatingE-UTRAN frequency division duplex (FDD) bands in 3GPP TS 36.101 is about20, and the MS may support multiple operating E-UTRA bands, anunrestricted undirected attempt to identify E-UTRAN frequencies mayimpact MS battery life and increase cell selection or reselection time.Within a PLMN, there could be a fixed number of operating E-UTRAN bandsor within a certain area corresponding to a list of TAs, the number ofavailable E-UTRAN frequencies is limited. Therefore, in the case wherechange of serving cell away from E-UTRAN is directed by the network, thefrequencies to search may be limited, for example to those indicated bythe corresponding mobility command or the system information transmittedfrom the E-UTRAN cell which served the MS before the serving cellchange. For example, a MobilityfromEUTRANCommand message can be extendedto include a set of E-UTRA frequencies. The MS stores and uses them forattempting to identify E-UTRAN cells. The MS may use the stored E-UTRANfrequencies received in the System Information Block Type 5 for theundirected or directed searches. The MS may store and use the E-UTRAfrequencies in the existing IdleModeMobilityControlInfo IE (informationelement) indicated by the RRC Connection Release message for theundirected or directed searches.

In the particular case of a CSFB procedure, in some CSFB situations,there may be a call back immediately after the termination of theoriginal CSFB call. In order to avoid rapidly alternating betweenE-UTRAN and the CS-supporting RATs, a timer may be started by the MS(whether it is indicated or not by the network is optional). The timerstarts upon completion of a CSFB call. The MS may wait for the timer toexpire before performing undirected or directed searching and/orreselection to an E-UTRAN cell.

In additional embodiments, the permission to perform undirected ordirected searching may be updated or changed over time. An updatedpermission may change whether and/or how the MS conducts an undirectedor directed search. The permission to perform undirected or directedsearching may be changed in any form of message from the network to theMS, such as but not limited to a broadcast, multicast, or point to pointsignaling message, may be updated via an OMA (Open Mobile Alliance) DM(Device Management) object broadcast over the air or other over the airor manual provisioning updates by the operator. Thus, as networkconfigurations change, an operator may enable or disable undirected ordirected searching in the MS, or otherwise modify or update how the MSconducts undirected or directed searching. The permission to performundirected or directed searching may be dedicatedly signaled from acorresponding E-UTRAN or GERAN. The permission to perform undirected ordirected searching may be updated periodically.

The embodiments also contemplate receiving a permission to perform anundirected search (or selection, as described below) in the form of afirst identifying characteristic of a cell of a third RAT. The third RATmay be a GERAN. The first identifying characteristic is associated witha second identifying characteristic used by cells of a first RAT (whichmay be an E-UTRAN). This embodiment describes the case where the MS ison UTRAN coverage, and the UTRAN access node sends an E-UTRAN indicativeARFCN in its GERAN NCL. The case of a MS on a GERAN cell with theE-UTRAN indicative ARFCN in its GERAN NCL may be described by providingthat the third RAT (such as a UTRAN) is the same as a second RAT (suchas a GERAN).

Permission To Perform Reselection:

The embodiments described above provide illustrative rules and policiesfor a MS to perform undirected or directed searching. However, inaddition, rules or policies may be provided on which the MS bases adetermination whether to report measurements of E-UTRAN cells(s) and/orto perform reselection to an E-UTRAN cell discovered while the MS isconstrained. Permission(s) to reselect an E-UTRAN cell may be either thesame as, or independent of, the permission(s) to the MS to conduct anundirected or directed search, or may be combinations thereof. Thesignaling for the two types of permission may use the same or differentsignaling rules, or combinations thereof. Either type of permission maybe changed or may vary over time, or may be static.

For embodiments which refer to indications or rules transmitted by anetwork, such rules may indicate that one or more additional criteriaare useful or required. For example, with respect to combinations of theabove exemplary rules for undirected or directed searching, the previousserving cell might indicate that reselection is permitted towards thatcell if and only if it is the best (e.g. has the strongest receivedsignal strength) of any with the same center frequency. For embodimentswhich allow a MS to perform autonomous reselection to an E-UTRAN cell,the MS may perform an undirected attempt to identify E-UTRAN cellsoperating on one or more frequencies, based on frequencies previouslymeasured or stored while in E-UTRAN coverage, or by searching on thefrequency of the most recently observed or used E-UTRAN cell.

In an embodiment, the MS may perform reselection based on one or more ofthe exemplary rules described above with respect to determining whetherto perform an undirected or directed search. Combinations of these rulesmay, or may not, be the same as those used to determine whether toperform undirected or directed searching. Additionally, the respectiveindicated permissions may or may not be the same. Nevertheless, similarrules may be used alone or in combination to perform cell reselection.

In another embodiment, permission to perform cell reselection may beprovided by the detected E-UTRAN cell or by the original E-UTRAN cell.For example, a flag, bit token or other indicator may be set inbroadcast information provided in an E-UTRAN cell. This flag, bit tokenor other indicator indicates to the MS that it has permission toreselect the corresponding E-UTRAN cell. In another embodiment, theflag/bit token/indicator may be signaled point to point (over the air)to the MS.

In 3GPP TS 36.331, mobility from E-UTRAN is described in section 5.4.3.The mobility procedure covers both handover and cell change order (CCO).For a handover, the MobilityFromEUTRACommand message includes radioresources that have been allocated for the MS in the target cell. TheCCO is used for GERAN only. The MobilityFromEUTRACommand message mayinclude system information for the target cell. To indicate support forautonomous cell reselection back to E-UTRAN for the MS, a new parametermay be introduced in the MobilityFromEUTRACommand message. Thisparameter may allow the MS to perform cell reselection to E-UTRAN afterending a CSFB session in GERAN. Thus, the MobilityFromEUTRACommand maybe used to command handover or a cell change from E-UTRAN to another RAT(3GPP or non-3GPP). In this command a field may be added, for example,as part of the message sequence in the form of “Auto-ReselectAllowed”,ENUMERATED (true, fromTgtCellOnly,false) OPTION—need OP. The“Auto-ReselectAllowed” indicates whether or not the MS is permitted toautonomously reselect back to E-UTRAN when the voice/CS session in thetarget RAT is completed. An E-UTRAN neighbour cell list need not beincluded in the (then) serving cell's system information or transmittedto the mobile station in that cell. If “Auto-ReselectAllowed” is true,then the MS may perform reselection to E-UTRAN cells. If“Auto-ReselectAllowed” is fromTgtCellOnly, the MS may performreselection only if the MS has not changed serving cell since completingthe mobility from the E-UTRAN procedure. If “Auto-ReselectAllowed” isfalse, then the MS may not perform reselection to the E-UTRAN cells.

In yet another embodiment, permission to perform cell reselection may beprovided by existing cell reselection rules using specified parameters.The existing reselection rules for reselection to E-UTRAN cells mayrequire the knowledge of various parameters (see 3GPP TS 45.008 version8.2.0 sub-clause 6.6.6), some of which may be obtained only from theserving GERAN cell that was upgraded and configured for this purpose. Inthis embodiment, the MS performs cell reselection using theseparameters, if available, or some pre-defined parameters in the casewhere the parameters are not transmitted by the serving cell. In thecase where the cell change from E-UTRAN is controlled, such as byhandover or by cell change order, these parameters may be provided bythe E-UTRAN cell in the mobility command. In this case, the mobilitycommand could also include the parameters to permit a priority-basedreselection algorithm to be carried out in cases where the MS is servedby a GERAN cell that does not transmit the desired parameters. Forexample, MobilityFromEUTRANCommand may indicate a set of E-UTRANfrequencies and possibly their priorities for the directed searches. TheMS searches and camps on an E-UTRAN cell on the frequencies whosequality is better than a predefined value or a value indicated by theE-UTRAN cell when the voice/CS session in the GERAN or UTRAN cell iscompleted.

In still another embodiment, permission to perform cell reselection maybe provided by some other mechanism or process. For example, the MS mayonly select the most recent E-UTRAN cell on which the MS was camped. TheMS may also select a cell which operates on the same frequency as thatused by the E-UTRAN cell on which it was most recently camped. Othertechniques could be used as well.

Allowing a MS to identify and reselect an E-UTRAN cell based on anindication from the original E-UTRAN cell may be implemented as follows.After leaving dedicated mode or dual transfer mode following a CSfallback procedure, a MS may attempt to identify, and (if identified)reselect an E-UTRAN cell if allowed to do so according to theAuto-ReselectAllowed IE included in the MobilityfromEUTRACommand message(see 3GPP TS 36.331). The MS may not perform such a reselection within afirst time, such as a number of seconds, after leaving the dedicatedmode, or within a second time, such as a number of seconds, if the callwas an emergency call. Thus, in an embodiment, the MS may be configuredto delay a first time before reselecting to the cell of a first RAT,wherein the first time may be dependent on a type of service on thesecond RAT that was terminated.

In another example, a MS may attempt to identify an E-UTRAN cell and (ifidentified) reselect that cell if no E-UTRAN Measurement Parametersstructure is received in any instance of the SI2quater message or theMeasurement Information message and one or more of the followingapply: 1) The E-UTRAN Configuration Status field transmitted in theSystem Information Type 2 quater message indicates that the absence ofthe E-UTRAN Measurement Parameters structure does not necessarilyindicate the absence of neighbouring E-UTRAN cells (there is no suchindication in the known art—this facet is part of the embodiments); 2)One or more ARFCNs in the GSM Neighbour Cell lists corresponds to one ormore E-UTRAN frequencies (EARFCNs); 3) One or more ARFCNs in the GSMNeighbour Cell lists explicitly confers permission to search and (ifidentified) reselect an E-UTRAN cell; or 4) [Non-CSFB case] the mostrecent serving cell before the current serving cell was an E-UTRAN celland the system information [or other point-to-point information]transmitted in that cell indicated that such reselection is permitted.

The MS may receive an E-UTRAN configuration status field. This fieldindicates the configuration status of the E-UTRAN neighbour cell list.For example, if set to “1,” this field indicates that the absence of theE-UTRAN Measurement Parameters structure indicates the absence ofneighbouring E-UTRAN cells. If set to “0,” the absence of the E-UTRANMeasurement Parameters structure does not necessarily indicate theabsence of neighbouring E-UTRAN cells.

The ARFCN to EARFCN mapping may be implemented in the following manner.An E-UTRAN ARFCN Mapping Description structure indicates that thepresence of specific ARFCNs in a GSM neighbour cell list (which are notused for GSM cells) indicates the presence of neighbour cells on one ormore of the E-UTRAN frequencies, identified by either an EARFCN orE-UTRAN Frequency Index.

In a particular non-limiting embodiment, the following code may beexemplary:

< E-UTRAN ARFCN Mapping Description structure > ::=   {1       ARFCN :bit (10) >       { 1 < EARFCN : bit (16) > } ** 0       { 1 <E-UTRAN_FREQUENCY_INDEX : bit(3) > }** 0 } ** 0;

Alternatively, E-UTRAN frequencies may be indicated by the presence ofone or more GSM ARFCNs, each of which corresponds to one or more E-UTRANfrequencies. In this case, the MS shall not include E-UTRAN parameterswithin measurement reports, but may report the strongest E-UTRANneighbour cell by means of its corresponding GSM ARFCN. The receivedsignal strength indication (RSSI) value to use in such a case may beimplementation-specific.

If the list of GSM frequencies in a neighbour cell list includes one ormore frequencies which are known to correspond to one or more E-UTRANfrequencies (EARFCNs), then the mobile station may build the E-UTRANneighbour cell list as if those ARFCNs corresponded to E-UTRANfrequencies. The E-UTRAN neighbour cell list may apply only to amulti-RAT MS supporting E-UTRAN. One or more instances of the SI2quatermessage may provide E-UTRAN frequencies, and zero or more not allowedphysical layer cell identities for each E-UTRAN frequency.Alternatively, E-UTRAN frequencies may be indicated by the presence ofone or more GSM ARFCNs, each of which corresponds to one or more E-UTRANfrequencies. The E-UTRAN frequencies define the E-UTRAN neighbour celllist. The E-UTRAN neighbour cell list may contain up to 8 frequencies,possibly more. The MS behavior is not specified if the number of E-UTRANfrequencies exceeds the MS monitoring capabilities, as defined in 3GPPTS 45.008.

FIG. 2 is a diagram illustrating a wireless communication system,according to an embodiment of the disclosure. Reference numerals commonto FIG. 2 and FIG. 1 refer to substantially similar objects. Forexample, FIG. 2 is similar to FIG. 1 in that the MS 100 is shown aspossibly being in communication with both an E-UTRAN cell 104 and aGERAN/UTRAN cell 108.

As mentioned above, an MS may base its decision to perform undirected ordirected searches and/or reselection on the reception of anE-UTRAN-indicative ARFCN. Details of this procedure will now beprovided. In this embodiment, while an MS is in an E-UTRAN cell, the MSis provided with one or more identifiers that are valid but unused in anon-E-UTRAN network (for example, in a GERAN or UTRAN network). Theidentifiers are or can be associated with the carrier frequencies forthe current E-UTRAN cell and possibly one or more other E-UTRAN cells.If the MS later enters a GERAN/UTRAN cell, the MS might be provided witha neighbour cell list for cells near the GERAN/UTRAN cell. If theneighbour cell list includes one or more of these E-UTRAN indicativeidentifiers (i.e. valid identifiers for the current network but that areassociated with E-UTRAN cells), the MS knows to attempt to identify, andpossibly reselect, those E-UTRAN cells.

More specifically, the identifiers might be unused broadcast controlchannel (BCCH) absolute radio frequency channel numbers (ARFCNs) for oneor more GERAN/UTRAN cells. One of skill in the art will recognize that aplurality of ARFCNs might be available to identify the GERAN/UTRAN cellsin a given geographic region, but that all of the available ARFCNs arenot necessarily used. In some cases, the ARFCNs might be numbered from 0through 1023, where ARFCNs 0 through 800 are valid and ARFCNs 801through 1023 are not valid. As used herein, the term “valid but unusedARFCN” might refer to an ARFCN numbered 801 through 1023, to an ARFCNnumbered 0 through 800 that is not currently in use in a givengeographic region, or to any other ARFCN that is not currently in use ina given geographic region.

In an embodiment, at least one valid but unused ARFCN is mapped to thecarrier frequency for at least one E-UTRAN cell. Such an ARFCN can bereferred to as an E-UTRAN-indicative ARFCN. An MS that is aware of themapping can attempt to identify the E-UTRAN cell with the mapped carrierfrequency when the mapped ARFCN appears in a neighbour cell listprovided to the MS.

An example of this embodiment is illustrated in FIG. 2, where the MS100, E-UTRAN access node 102, E-UTRAN cell 104, GERAN/UTRAN access node106, and GERAN/UTRAN cell 108 as shown in FIG. 1 are again depicted.When the MS 100 is present in the E-UTRAN cell 104, the E-UTRAN accessnode 102 provides the MS 100 with information 110 related to one or morevalid but unused ARFCNs. In some cases, the information 110 associatesat least one valid but unused ARFCN with at least one E-UTRAN frequency.In other cases, the information 110 is a valid but unused ARFCN that theMS 100 can associate with an E-UTRAN frequency. In yet other cases, theinformation 110 is a valid but unused ARFCN that indicates generalpermission for undirected searching and possibly reselection.

In the illustrated embodiment, the information 110 is a map in which oneor more ARFCNs are associated with the carrier frequencies for one ormore E-UTRAN cells. Each entry 212 of the map ties an unused ARFCN 214to the carrier frequency 216 of an E-UTRAN cell. More than one E-UTRANcell may use each of the E-UTRAN frequencies 216, and more than oneE-UTRAN frequency 216 could be mapped to one ARFCN 214. In anotherembodiment, as described in detail below, rather than providing a map tothe MS 100, the E-UTRAN access node 102 provides the MS 100 withinformation with which the MS can create a map. In another embodiment,as described in detail below, the ARFCNs 214 indicate permission toperform undirected or directed searches and possibly reselection. In anyof these cases, the information that the E-UTRAN access node 102provides to the MS 100 will be referred to herein as the ARFCN/E-UTRANinformation 110. The ARFCN/E-UTRAN information 110 can be provided tothe MS 100 using one of several different techniques, as describedbelow. Also, in some cases, the MS 100 might store the associationbetween at least one unused ARFCN and at least one E-UTRAN frequency forlater use.

In an embodiment, if the MS 100 later connects to the GERAN/UTRAN accessnode 106, the GERAN/UTRAN access node 106 can send the MS 100 aneighbour cell list 120 that might include one or more of the ARFCNs 214that were included in the ARFCN/E-UTRAN information 110. Standardoperations and maintenance procedures might be used to configure theGERAN/UTRAN access node 106 to be able to broadcast the neighbour celllist 120 to the MS 100. In this manner, the GERAN/UTRAN access node 106would not need to be upgraded in order to be able to provide the MS 100with one or more of the ARFCNs 214 that were included in theARFCN/E-UTRAN information 110.

If the MS 100 attempts to leave the GERAN/UTRAN cell 108, the MS 100 cancompare the ARFCN entries 222 in the neighbour cell list 120 to theARFCN entries 214 in the ARFCN/E-UTRAN information 110. If one or moreof the ARFCN entries 222 in the neighbour cell list 120 match one ormore of the ARFCN entries 214 in the ARFCN/E-UTRAN information 110, theMS 100 knows that the frequencies 216 associated with those ARFCNentries 214 are the center frequencies for E-UTRAN cells. The MS 100 canthen use those E-UTRAN frequencies 216 to attempt to identify an E-UTRANcell. If an E-UTRAN cell is identified, the techniques described abovemight be used to determine whether the MS 100 connects to the E-UTRANcell. In this manner, the MS 100 might be able to connect to the E-UTRANcell 104 or another E-UTRAN cell after becoming constrained in theGERAN/UTRAN cell 108. This technique might be used instead of or inaddition to the techniques described above for a MS to attempt toidentify and reselect an E-UTRAN cell after becoming constrained in aGERAN/UTRAN cell.

As mentioned above, the E-UTRAN access node 102 might provide theARFCN/E-UTRAN information 110 to the MS 100 using various techniques. Inan embodiment, non-access stratum (NAS) signaling is used to provide theARFCN/E-UTRAN information 110 to the MS 100. That is, associations aremade in the E-UTRAN core network (also known as the evolved packet coreor EPC) between one or more ARFCNs 214 and one or more E-UTRANfrequencies 216. The resulting map could then be given to the MS 100when the MS 100 attaches to the EPC. Such NAS signaling may occur whenthe MS 100 moves from one cell to another and/or at periodic intervals.In this manner, the ARFCN/E-UTRAN information 110 could be provided tothe MS 100 by making only minimal upgrades to the core network elements.Modifications would not be needed for the access nodes.

In other embodiments, access stratum (AS) signaling is used to providethe ARFCN/E-UTRAN information 110 to the MS 100. In these cases, anaccess node transmits the ARFCN/E-UTRAN information 110 over the air tothe MS 100. In one embodiment, the E-UTRAN access node 102 broadcasts anARFCN 214 in its system information. When the MS 100 receives thebroadcast, the MS 100 associates the ARFCN 214 with the E-UTRA ARFCN(EARFCN) of the current cell 104. The MS 100 might store the associationbetween the ARFCN and the E-UTRAN frequency so that the E-UTRANfrequency can be used later if the MS 100 becomes constrained in aGERAN/UTRAN cell.

Alternatively, the E-UTRAN access node 102 broadcasts, multicasts, orpoint-to-point transmits a list of ARFCNs 214 and a list of associatedE-UTRAN frequencies 216. Other cell reselection parameters could also betransmitted, such as a minimum quality threshold for reselection to anE-UTRAN cell. The MS 100 could receive this information and store it forlater use. In other embodiments, a GERAN/UTRAN access node with advancedcapabilities could transmit such information.

In another embodiment, a single E-UTRAN-indicative ARFCN 214 mightindicate permission for undirected searching or for both undirectedsearching and reselection. Alternatively, one E-UTRAN-indicative ARFCN214 might indicate permission for undirected searching and anotherE-UTRAN-indicative ARFCN 214 might indicate permission for reselection.

In an embodiment, the ARFCN/E-UTRAN information 110 might be valid onlywithin a limited scope. For example, the ARFCN/E-UTRAN information 110might be valid only for a limited time or only within a limitedgeographic region. Alternatively or in addition, the ARFCN/E-UTRANinformation 110 might be valid only within certain cells. For instance,in the case where the mapping was provided by NAS, the ARFCN/E-UTRANinformation 110 might be applicable only in the cell in which theARFCN/E-UTRAN information 110 was provided to the MS 100. Alternatively,the ARFCN/E-UTRAN information 110 might be applicable only in cellsoperated by the same operator that operates the cell in which theARFCN/E-UTRAN information 110 was provided to the MS 100 or only incells within the same location area or tracking area, or within the samePLMN or equivalent PLMN as that in which the information 110 wasreceived.

In various embodiments, an ARFCN 214 that is mapped to an E-UTRANfrequency 216 could be used according to various different techniques.For example, when the MS 100 is in a GERAN/UTRAN cell and measures thequality parameters of one or more neighbouring E-UTRAN cells, the MS 100could use the ARFCNs 214 associated with the E-UTRAN cells to inform theGERAN/UTRAN access node of the center frequency or frequencies of theE-UTRAN cells on which the measurements were performed. Also, when theMS 100 intends to move to one of the neighbouring E-UTRAN cells, the MS100 could use the ARFCN 214 associated with that E-UTRAN cell to informthe GERAN/UTRAN access node of the center frequency or frequencies ofthe E-UTRAN cell to which the MS 100 intends to move.

In addition, when the GERAN/UTRAN access node is informed that the MS100 intends to move to an E-UTRAN cell associated with one of the unusedbut valid ARFCNs 214, the GERAN/UTRAN access node can use the receivedARFCN 214 to confirm to the MS 100 that the MS 100 can continuereselection. Also, the GERAN/UTRAN access node can order the MS 100 toreselect an E-UTRAN cell and can use an ARFCN 214 to identify thecarrier frequency of the E-UTRAN cell to which the MS 100 should move.

In yet another embodiment, the E-UTRAN indicative ARFCN information 110might be received by an MS that is capable of recognizing that this isan E-UTRAN indicative ARFCN, but the MS is not capable of connecting toE-UTRAN cells. Such an MS might be provided with logic such that uponreceiving an E-UTRAN-indicative ARFCN 214, the MS refrains fromsearching for a GERAN/UTRAN cell that is associated with theE-UTRAN-indicative ARFCN 214. Since the ARFCN is valid but unused in theGERAN/UTRAN system, no such GERAN/UTRAN cell exists, and therefore theMS would not be able to connect to a cell that is associated with thisARFCN. Prohibiting this search could save battery and processing powerthat the MS might otherwise waste by attempting to connect to such acell. The E-UTRAN indicative ARFCN/E-UTRAN information mapping 110 couldbe provisioned to such an MS through NAS signaling or in some othermanner.

FIG. 3 is a flowchart illustrating a process of a MS performingundirected searching and subsequent reselection, according to anembodiment of the disclosure. The process shown in FIG. 3 may beimplemented in a MS, such as MSs 100, 110A, or 110B in FIG. 1. Theprocess system 300 shown in FIG. 3 may be implemented according to thedevices and methods described with respect to FIG. 1 and/or FIG. 2. Inan embodiment, the method shown in FIG. 3 is implemented in a MS enabledto communicate with both an evolved universal terrestrial radio accessnetwork (E-UTRAN) and a general packet radio service/enhanced data ratesfor global evolution radio access network (GERAN).

The process begins as a MS becomes constrained on a GERAN/UTRAN cell(block 300). The MS receives permission to perform an undirected ordirected attempt to identify an E-UTRAN to attempt to identify theE-UTRAN (block 302). In an embodiment, the permission is received beforethe MS becomes constrained on the GERAN/UTRAN cell. In anotherembodiment, receiving permission includes the permission beingprovisioned into the device by the network operator prior to the devicebeing used in a live network. In another embodiment, receivingpermission includes the permission being stored in a memory of thedevice at the time of device manufacture or at any other time andretrieved from memory to be used by the MS at any time. The term“receiving permission” includes the MS receiving permission in thismanner before becoming constrained. Subsequently, the MS may (dependingon the permission) begin the undirected or directed attempt to identifythe E-UTRAN, which could be one or more E-UTRAN cells (block 304).

Optionally, before conducting the undirected search, the MS performs acircuit switched (CS) fallback service, which is the cause for the MSbecoming constrained. In this case, the undirected search is responsiveto terminating the CS fallback service.

Optionally, the permission is received from a previous serving E-UTRANcell. Optionally, the permission is received from a GERAN or UTRAN cell.

In another embodiment, the permission is received in the form of anindicative E-UTRAN ARFCN. In this case, the indicative E-UTRAN ARFCN isidentified via a mapping as an E-UTRAN absolute radio frequency channelnumber (EARFCN). In another embodiment, the permission is received inthe form of an indicative E-UTRAN ARFCN, but this ARFCN does not map toan E-UTRAN frequency, but rather is a general indicator.

Permission to perform reselection may be based on dedicated prioritiespreviously received by the MS. The permission may be stored on at leastone of a subscriber identity module (SIM) and a memory of the MS priorto the MS becoming constrained.

In another embodiment, the permission may be based on at least one of amobility change and a cell change. In this case, the permission may bebased on a number of cell changes since the MS was last served by anE-UTRAN cell. Alternatively, the permission is based on the MS being inthe same location area or routing area as when the MS initially leftE-UTRAN service. Alternatively the permission may be based on othermobility factors, such as but not limited to absolute locationdetermined by location information in the MS (e.g. as could be obtainedusing GPS) or a velocity of mobility information for example.

In yet another embodiment, the permission is communicated by non-accessstratum (NAS) signaling. The permission may be received from user input.The permission may be received responsive to the MS successfullyperforming a recent combined attach procedure in an evolved packetsystem (EPS). The permission may be received responsive to the MS beingcapable of internet protocol multimedia subsystem (IMS) voice service.

Returning to FIG. 3, optionally, the MS may receive a second permissionto perform cell reselection or reselection to the identified E-UTRANcell (block 306). The process terminates thereafter. The term “receivingsecond permission” includes the MS receiving permission in this mannerbefore becoming constrained. In fact the second permission may bereceived in any of the ways in which the first permission may bereceived. The second permission may be received from the target E-UTRANcell. The second permission may be a flag, bit token or other indicatorset in broadcast information. Alternatively, the flag/bittoken/indicator may be signaled point to point to the MS. The secondpermission may be the same as the first permission. The secondpermission may be a reselection rule stored in the MS. The secondpermission may be such that the MS may only select the most recentE-UTRAN cell on which the MS was camped. In an embodiment, the MS maystore the second permission in memory. In an embodiment, the permissionmay be received after reselection, that is that the MS needs to attemptreselection to an E-UTRAN cell and then will learn from the reselectedcell whether or not it has permission to camp on it. In an embodiment,the MS may receive a third permission (which may be independent or partof the second permission or part of the first permission) to measure theE-UTRAN cell or cells. The third permission allows the MS to measure andthen report these measurements back to the E-UTRAN and/or theGERAN/UTRAN.

FIG. 4 is a flowchart illustrating a method for granting a MS permissionto search one or more E-UTRAN frequencies while in a GERAN cell,according to an embodiment of the disclosure. The process 400 shown inFIG. 4 may be implemented in a MS, such as MSs 100, 110A, or 110B inFIG. 1. The process shown in FIG. 4 may be implemented according to thedevices and methods described with respect to FIG. 2. In an embodiment,the method shown in FIG. 4 is implemented in a MS enabled to communicatewith both an evolved universal terrestrial radio access network(E-UTRAN) and a GSM/EDGE radio access network (GERAN).

In an embodiment, the process takes place in a mobile station capable ofidentifying a cell of a first RAT while being served by a cell of asecond RAT. The process begins as the mobile station receives a list ofneighbour cells of the second RAT, the list containing at least oneidentifying characteristic associated with at least one cell of thefirst RAT (block 410). The mobile station then identifies a cell of thefirst RAT associated with the at least one identifying characteristic(block 420). The process terminates thereafter.

The embodiments described herein are proposed for GERAN, UTRAN, andE-UTRAN networks. However, the embodiments are equally applicable forany combination of radio access technologies where asymmetry in mobilityprocedures, neighbour cell lists, or other features gives rise to a MSbecoming constrained. Thus, the embodiments apply to any situation inwhich a MS is constrained in a first network type and desires to connectto a second network type.

FIG. 5 is a flowchart illustrating a method for granting an MSpermission to search one or more E-UTRAN frequencies while in a GERANcell, according to an embodiment. The process shown in FIG. 5 may beimplemented in an MS, such as MSs 100, 110A, or 110B in FIG. 1. Theprocess 500 shown in FIG. 5 may be implemented according to the devicesand methods described with respect to FIG. 2. In an embodiment, themethod shown in FIG. 5 is implemented in an MS enabled to communicate inboth E-UTRAN and GERAN/UTRAN.

The process begins at block 570, where an MS is provided with anE-UTRAN-indicative ARFCN indicating that the MS has permission toattempt to identify an E-UTRAN cell, measure and report the E-UTRAN,and/or reselect to an E-UTRAN cell. At block 580, based on thepermission(s) granted, the MS attempts to identify, measure and report,and/or reselect at least one E-UTRAN cell.

FIG. 6 is a block diagram illustrating a MS communicating with a corenetwork via a radio access network, according to an embodiment of thedisclosure. In an illustrative embodiment, a MS 600, which could be orMS 100 or MS 110A/B of FIG. 1, attempts to establish a connection with aCN 602. Such an attempt can be referred to as a mobile originating call,or MO, because the MS initiates the connection attempt. However, thefollowing processes can also apply to a mobile terminating (MT) call,wherein the CN 602 initiates the connection attempt.

To initiate the connection attempt, the MS NAS 604 sends a requestmessage, e.g., a SERVICE REQUEST or EXTENDED SERVICE REQUEST, to the CNNAS 606 via a radio access network (RAN) 608. The MS NAS 604 initiatesthe request and, within the MS 600, transmits the request to the MSaccess stratum (AS) 610. In turn, the AS 610 transmits the request overa physical layer, such as radio waves as shown by arrow 612, to the RAN608.

The RAN AS 614 receives the request, and allocates preliminary resourcesto the MS 600 and then communicates the request to interworkingfunctions 616 of the RAN 608. Interworking functions may includemanaging the request relative to other requests, as well as otherfunctions. Interworking functions 616 also communicate with CN to RANcontrollers 618, which control communications between the RAN 608 andthe CN 602. The actual communication of the request between the RAN 608and the CN 602 is transmitted along a physical layer, which may be wiresor cables, for example, as shown by arrow 620. The physical layer 620can also be implemented as a wireless backhaul.

Within the CN 602, CN to RAN controllers 622 receive the request andtransmit the request to the CN NAS 606. The CN NAS 606 then decodes thedata within the request, and takes an appropriate action to allocateadditional or necessary mobile resources to the MS 600 for that wirelesscommunication. The CN NAS 606 transmits such information to the MS 600via the RAN 608 in a manner similar to the process described above, butin the other direction.

In another embodiment, the CN initiates a MT (mobile terminating) call.The process described above occurs from CN NAS 606 to MS NAS 604 in aprocess similar to that described above.

Within the context of FIG. 1 and FIG. 6, a CSFB (circuit switchedfallback) procedure may be understood. CS fallback in EPS enables voiceand other CS domain services by reusing networks that have the CSinfrastructure when the MS is initially served by an E-UTRAN network.Examples of networks that have the CS infrastructure include GERAN andUTRAN networks. Thus, a CSFB enabled MS connected to an E-UTRAN networkmay use GERAN or UTRAN networks to establish one or more CS domainservices. CS fallback is used where coverage of E-UTRAN and GERAN/UTRANRANs overlap.

A CSFB capable MS also supports combined procedures for EPS/IMSI attach,update, and detach functions. These procedures allow the terminal to beregistered both with an MME, for packet switched domain servicesprovided using the E-UTRAN network, and with an MSC and MME to create anassociation between them based on the fact that the MS is simultaneouslyregistered with each of them.

CSFB calls generally fall into two types: a mobile originating (MO) calland a mobile terminating (MT) call. The first type of CSFB call is amobile originating call, in which the MS initiates a CSFB call. For theMO call, when the MS is in E-UTRAN and desires to make a CSFB call oruse CS services, the MS sends an Extended Service Request with the CSFBindicator to the MME. The MS may only transmit this request if the MS isattached to a CS domain and has previously registered with an MSC.

The MME sends a message to the eNB that indicates that the MS should bemoved to UTRAN/GERAN. At this point, the eNB may optionally solicit ameasurement report from the MS to determine the target cell in the GERANor UTRAN. If packet switched handover in GERAN is supported, then eNBtriggers a packet switched handover to a GERAN/UTRAN neighbour cell bysending a Handover Required message to the MME. Then, an inter-RAThandover from E-UTRAN to UTRAN or GERAN begins, as specified in 3GPP TS23.401. As part of this handover, the MS receives a HO from E-UTRANcommand and tries to connect to a cell in the target RAT. This commandmay contain a CSFB Indicator which tells the UE that the handover istriggered due to a CSFB request.

Alternatively (e.g. if PS handover is not supported in GERAN), then theeNB triggers an inter-RAT cell change order, optionally with NACC, tothe GERAN cell by sending an RRC message to the MS. The inter-RAT cellchange order may contain a CSFB Indicator which indicates to the MS thatthe cell change order is triggered due to a CSFB request. If theinter-RAT cell change order contains a CSFB Indicator, and the MS failsto establish connection to the target RAT, then the MS considers thatthe CSFB procedure has failed. A Service Request procedure is consideredto be successfully completed when the cell change order procedure iscompleted successfully.

In GERAN A/Gb mode, the MS established a radio relay connection by usingthe procedures specified in 3GPP TS 44.018. The MS requests and isassigned a dedicated channel. Once the CS resources have been allocatedin the GERAN cell, and the main signaling link is established asdescribed in 3GPP TS 44.018, the MS enters a Dual Transfer Mode (ifsupported by both the MS and the new cell) or Dedicated Mode. The CScall establishment procedure then completes.

If the MSC serving the GERAN/UTRAN cell is different from the MSC thatserved the MS when it was camped on E-UTRAN, then the MSC will rejectthe service required unless an implicit location update is performed.When the target system operates in Network Mode of Operation (NMO) 1,then if the MS is still in UTRAN/GERAN after the CS voice call isterminated, and if a combined RA/LA update has not already beenperformed, then the MS performs a combined RA/LA update procedure. Thisprocedure is used to create an association between the MSC and the SGSNand to release the association between the MSC and the MME.

Once the CS services end in the CS domain, the MS may move back toE-UTRAN by means of mobility mechanisms described above with respect toFIG. 1 through FIG. 4. The MS may then send a NAS message, such as aService Request or TAU, to the MME. If the MS context in the MMEindicates that the MS is in suspended status, the MME sends a ResumeRequest (IMS) message to the S-GW that request the resumption of EPSbearers for the MS. The S-GW acknowledges the Resume Request and clearsthe MS's suspending status, and the NAS message is processedaccordingly.

The second type of CSFB call mentioned above is a mobile terminating(MT) call, in which a CSFB call is placed to the MS. For a MT CSFB call,the paging message is sent to the MME from the MSC, including locationinformation necessary or desirable to page the terminal. Thisinformation is sent to one or more eNBs. Upon receiving the page, the MSestablishes an RRC connection and sends an Extended Service Request(with CSFB indicator) to the MME. The MME then sends parameters to theeNB in order to move the MS to UTRAN/GERAN. The eNB may optionallysolicit measurement reports from the MS to determine the target cell towhich the MS should be redirected.

After that, the eNB releases the RRC connection with redirectioninformation to change to a CS capable RAT. As an option, systeminformation corresponding to the target cell might be provided by theeNB. In this case, the MS receives an inter-RAT cell change order thatmay contain a CSFB indicator. If the LA/RA information of the new cellis different from the one stored in the MS, and if the target systemoperates in NMO1, then the MS performs a combined RA/LA procedure. Ifthe target system does not operate in NMO1, then the MS performs a LAU.

The MS responds with a page response message to the MSC in the new RATand then enters either DTM or Dedicated Mode (if in GERAN) orRRC_CONNECTED mode (if in UTRAN), and the CS call establishmentprocedure completes. If the MS is still in UTRAN/GERAN after the CSvoice call is terminated, and if a LAU or a combined RA/LA update hasnot already been performed in the call establishment phase, then the MSperforms either a LAU or the combined procedure. The mobility fromE-UTRAN to the CS-capable RAT, particularly in the case of UMTS, mayalso be performed by means of a PS Handover procedure in a mannersimilar to that described for the MO call.

The details of a CS fallback communication procedure in mobilecommunication systems prior to LTE/EPS—such as UMTS—may not be necessaryto an understanding of the present disclosure. For example, a MS mightbecome constrained in situations other than in CS fallback procedures.The embodiments contemplate procedures for allowing the MS to reconnectto an E-UTRAN or other LTE network regardless of the manner in which theMS became constrained on a GERAN network.

The MS and other components described above might include a processingcomponent that is capable of executing instructions related to theactions described above. FIG. 7 illustrates an example of a system 715that includes a processing component 710 suitable for implementing oneor more embodiments disclosed herein. In addition to the processor 710(which may be referred to as a central processor unit or CPU), thesystem 700 might include network connectivity devices 720, random accessmemory (RAM) 730, read only memory (ROM) 740, secondary storage 750, andinput/output (I/O) devices 760. These components might communicate withone another via a bus 770. In some cases, some of these components maynot be present or may be combined in various combinations with oneanother or with other components not shown. These components might belocated in a single physical entity or in more than one physical entity.Any actions described herein as being taken by the processor 710 mightbe taken by the processor 710 alone or by the processor 710 inconjunction with one or more components shown or not shown in thedrawing, such as a digital signal processor (DSP) 790. Although the DSP790 is shown as a separate component, the DSP 790 might be incorporatedinto the processor 710.

The processor 710 executes instructions, codes, computer programs, orscripts that it might access from the network connectivity devices 720,RAM 730, ROM 740, or secondary storage 750 (which might include variousdisk-based systems such as hard disk, floppy disk, or optical disk).While only one CPU 710 is shown, multiple processors may be present.Thus, while instructions may be discussed as being executed by aprocessor, the instructions may be executed simultaneously, serially, orotherwise by one or multiple processors. The processor 710 may beimplemented as one or more CPU chips.

The network connectivity devices 720 may take the form of modems, modembanks, Ethernet devices, universal serial bus (USB) interface devices,serial interfaces, token ring devices, fiber distributed data interface(FDDI) devices, wireless local area network (WLAN) devices, radiotransceiver devices such as code division multiple access (CDMA)devices, global system for mobile communications (GSM) radio transceiverdevices, worldwide interoperability for microwave access (WiMAX)devices, and/or other well-known devices for connecting to networks.These network connectivity devices 720 may enable the processor 710 tocommunicate with the Internet or one or more telecommunications networksor other networks from which the processor 710 might receive informationor to which the processor 710 might output information. The networkconnectivity devices 720 might also include one or more transceivercomponents 725 capable of transmitting and/or receiving data wirelessly.

The RAM 730 might be used to store volatile data and perhaps to storeinstructions that are executed by the processor 710. The ROM 740 is anon-volatile memory device that typically has a smaller memory capacitythan the memory capacity of the secondary storage 750. ROM 740 might beused to store instructions and perhaps data that are read duringexecution of the instructions. Access to both RAM 730 and ROM 740 istypically faster than to secondary storage 750. The secondary storage750 is typically comprised of one or more disk drives or tape drives andmight be used for non-volatile storage of data or as an over-flow datastorage device if RAM 730 is not large enough to hold all working data.Secondary storage 750 may be used to store programs that are loaded intoRAM 730 when such programs are selected for execution.

The I/O devices 760 may include liquid crystal displays (LCDs), touchscreen displays, keyboards, keypads, switches, dials, mice, track balls,voice recognizers, card readers, paper tape readers, printers, videomonitors, or other well-known input/output devices. Also, thetransceiver 725 might be considered to be a component of the I/O devices760 instead of or in addition to being a component of the networkconnectivity devices 720.

The following are incorporated herein by reference for all purposes: 3rdGeneration Partnership Project (3GPP) Technical Specifications (TS)23.272, 23.401, 36.101, 36.331, 44.018, 44.060, 45.005, and 45.008.

A generic access network (GAN) may use an ARFCN to identify a GANcontroller in those cases where a MS is connected via an internetprotocol (IP) network, rather than by a radio access network (RAN) suchas GERAN, UTRAN, etc., which is the type of network used by mostwireless communication devices. However, the use of a GSM ARFCN in thiscase does not address the possibility of a MS becoming constrained forthe following reasons: 1) in the GAN case, the use of an ARFCN isprimarily to permit measurement reports and voice handovers to betriggered without any upgrade to the GERAN network; 2) the coverage of aGAN network is not known to the operator, since GAN coverage istypically provided by means of wireless communications using unlicensedspectrum (e.g. by means of IEEE 802.11 communications), where the accesspoints are not owned by the operator and hence their location may not beknown; and 3) connectivity to an 802.11 access point or other IP networkdoes not necessarily mean that connectivity to the GANC is possible.Therefore, there exists a disconnect between the radio level coverageand the meaning of the ARFCN. In fact, the ‘undirected search’ for theGANC is based on knowledge in the MS of the GANC's IP address (orinternet host name), rather than the ARFCN indicated by a GERAN network.Hence, (critically) the presence of an ARFCN in a GERAN neighbour celllist which corresponds to a GANC is independent of the MS's process ofattempting to connect to the GANC. However, use of an ARFCN in an IPnetwork may not be useful for those situations in which a MS becomesconstrained, because no other unified addressing structure exists forGAN cells other than the ARFCN. ARFCN is the addressing scheme forGAN—whereas E-UTRAN does have an addressing scheme. The ARFCN for a GANnetwork identifies a physical box or router, whereas identifiers forE-UTRAN and GERAN networks identify cells. Because GAN networks aredifferent from E-UTRAN, and GERAN networks, the use of an ARFCN in GANnetworks is not related to the above-described solutions for a MS thatis constrained in a GERAN network and desires to connect to an E-UTRANnetwork.

Thus, the embodiments provide for a mobile station capable of beingserved via a first radio access technology (RAT) and a second RAT. Themobile station includes a component configured to receive a permissionto identify a cell of the first RAT in absence of a first radio accesstype neighbour cell list for a serving cell of the second RAT. Themobile station also includes a component configured to identify a cellof the first RAT after receiving the permission. In an embodiment, thefirst radio access type neighbour cell list for a serving cell of thesecond RAT can be an E-UTRAN neighbour cell list used in accordance with3GPP TS 44.018 and TS 45.008.

In another embodiment, a device, method, and a program on a computerreadable medium is provided for a mobile station that is capable ofbeing served via a first radio access technology (RAT) and a second RAT.The mobile station includes a component configured to receive apermission to identify a cell of the first RAT in absence of a firstradio access type neighbour cell list for a serving cell of the secondRAT. The mobile station also includes a component configured to identifya cell of the first RAT after receiving the permission.

In yet another embodiment, a device, method, and a program on a computerreadable medium is provided for an access node. The access node includesa component configured to communicate with a mobile station operating onone of a first radio access technology (RAT) and a second RAT. Thecomponent is configured to communicate a permission to the mobilestation to attempt to identify a cell of the first RAT in the absence ofcommunicating to the mobile station a first radio access type neighbourcell list for a serving cell of the second RAT.

In still another embodiment, a device, method, and a program on acomputer readable medium are provided for granting a mobile stationpermission to attempt to identify a cell of a first radio accesstechnology (RAT) while being served by a cell of a second RAT. Themobile station receives a list of neighbour cells of the second RAT. Thelist contains at least one identifying characteristic associated with atleast one cell of the first RAT. The mobile station identifies a cell ofthe first RAT associated with the at least one identifyingcharacteristic.

In a further embodiment, a device, method, and program on a computerreadable medium are provided with respect to a mobile station incapableof communicating via a first radio access technology (RAT) and capableof communicating via a second radio access technology (RAT). A componentis configured to receive a list of neighbour cells of the second RAT.The list contains at least one identifying characteristic associatedwith at least one cell of the first RAT. A component is configured todetermine that the at least one identifying characteristic is associatedwith at least one cell of the first RAT.

While several embodiments have been provided in the present disclosure,it should be understood that the disclosed systems and methods may beembodied in many other specific forms without departing from the spiritor scope of the present disclosure. The present examples are to beconsidered as illustrative and not restrictive, and the intention is notto be limited to the details given herein. For example, the variouselements or components may be combined or integrated in another systemor certain features may be omitted, or not implemented.

Also, techniques, systems, subsystems and methods described andillustrated in the various embodiments as discrete or separate may becombined or integrated with other systems, modules, techniques, ormethods without departing from the scope of the present disclosure.Other items shown or discussed as coupled or directly coupled orcommunicating with each other may be indirectly coupled or communicatingthrough some interface, device, or intermediate component, whetherelectrically, mechanically, or otherwise. Other examples of changes,substitutions, and alterations are ascertainable by one skilled in theart and could be made without departing from the spirit and scopedisclosed herein.

1-21. (canceled)
 22. A method in a mobile station, the methodcomprising: establishing a connection with a cell of a first radioaccess technology (RAT); using the connection to perform, after theestablishing, a circuit switched (CS) communication procedure notavailable on a cell of a second RAT; terminating the CS communicationprocedure; and responsive to terminating the CS communication procedure,selecting a cell of the second RAT without receiving an indication ofexistence of any cell of the second RAT from the cell of the first RAT.23. The method of claim 22, wherein selecting a cell of the second RATincludes: responsive to terminating the CS communication procedure,starting a timer; and responsive to expiry of the timer, selecting thecell of the second RAT.
 24. The method of claim 22, wherein the firstRAT comprises a global system for mobile communications (GSM) network,an enhanced data rates for GSM evolution (EDGE) network, or a universalterrestrial radio access network (UTRAN), and wherein the second RATcomprises an evolved universal terrestrial radio access network(E-UTRAN).
 25. The method of claim 22, wherein the mobile station isserved by the cell of the first RAT before establishing the connection.26. The method of claim 22, wherein selecting a cell of the second RATincludes: determining that a most recent combined attach procedure to anevolved packet system (EPS) is successful; and responsive to terminatingthe CS communication procedure and the successful combined attachprocedure, selecting the cell of the second RAT.
 27. The method of claim22, wherein the CS communication procedure is used for a voicecommunication.
 28. The method of claim 22, wherein the CS communicationprocedure is a CS fallback procedure.
 29. A mobile station, comprising:a memory; and at least one hardware processor communicatively coupledwith the memory and configured to: establish a connection with a cell ofa first radio access technology (RAT); use the connection to perform,after establishment of the connection, a circuit switched (CS)communication procedure not available on a cell of a second RAT;terminate the CS communication procedure; and responsive to terminationof the CS communication procedure, select a cell of the second RATwithout receiving an indication of existence of any cell of the secondRAT from the cell of the first RAT.
 30. The mobile station of claim 29,wherein selection of a cell of the second RAT includes: responsive tothe termination of the CS communication procedure, start a timer; andresponsive to expiry of the timer, select the cell of the second RAT.31. The mobile station of claim 29, wherein the first RAT comprises aglobal system for mobile communications (GSM) network, an enhanced datarates for GSM evolution (EDGE) network, or a universal terrestrial radioaccess network (UTRAN), and wherein the second RAT comprises an evolveduniversal terrestrial radio access network (E-UTRAN).
 32. The mobilestation of claim 29, wherein the mobile station is served by the cell ofthe first RAT before establishment of the connection.
 33. The mobilestation of claim 29, wherein selection of the cell of the second RATincludes: determine that a most recent combined attach procedure to anevolved packet system (EPS) is successful; and responsive to terminationof the CS communication procedure and the successful combined attachprocedure, select the cell of the second RAT.
 34. The mobile station ofclaim 29, wherein the CS communication procedure is used for a voicecommunication.
 35. The mobile station of claim 29, wherein the CScommunication procedure is a CS fallback procedure.
 36. A non-transitorycomputer-readable medium containing instructions which, when executed,cause a mobile station to perform operations comprising: establishing aconnection with a cell of a first radio access technology (RAT); usingthe connection to perform, after the establishing, a circuit switched(CS) communication procedure not available on a cell of a second RAT;terminating the CS communication procedure; and responsive toterminating the CS communication procedure, selecting a cell of thesecond RAT without receiving an indication of existence of any cell ofthe second RAT from the cell of the first RAT.
 37. The non-transitorycomputer-readable medium of claim 36, wherein selecting a cell of thesecond RAT includes: responsive to terminating the CS communicationprocedure, starting a timer; and responsive to expiry of the timer,selecting the cell of the second RAT.
 38. The non-transitorycomputer-readable medium of claim 36, wherein the first RAT comprises aglobal system for mobile communications (GSM) network, an enhanced datarates for GSM evolution (EDGE) network, or a universal terrestrial radioaccess network (UTRAN), and wherein the second RAT comprises an evolveduniversal terrestrial radio access network (E-UTRAN).
 39. Thenon-transitory computer-readable medium of claim 36, wherein the mobilestation is served by the cell of the first RAT before establishing theconnection.
 40. The non-transitory computer-readable medium of claim 36,wherein selecting a cell of the second RAT includes: determining that amost recent combined attach procedure to an evolved packet system (EPS)is successful; and responsive to terminating the CS communicationprocedure and the successful combined attach procedure, selecting thecell of the second RAT.
 41. The non-transitory computer-readable mediumof claim 36, wherein the CS communication procedure is a CS fallbackprocedure.